REAL-SPACE DENSITY-MATRIX RENORMALIZATION-GROUP STUDY OF THE KONDO NECKLACE

A recently proposed density-matrix renormalization group is used to investigate the ground-state properties of the Kondo-necklace Hamiltonian. It represents a chain of XY interacting pseudospins that are Kondo coupled (J) to localized spins. The spin gap as well as the short- and long-range spin correlation functions are consistent with the existence of a smooth crossover at J0.5. For J≤0.5, the gap depends exponentially on J-1/2 and the in-plane correlation function of the localized spins shows RKKY oscillations while the z one falls monotonically in contrast to the XY behavior. The correlation length diverges at J=0. For J0.5, the gap is linearly increasing with J, and the system is made of nearly independent singlets. © 1995 The American Physical Society.